From U.S. Pat. No. 4,310,438, it is known to add water-soluble polyethyleneamines having at least one secondary amine and two primary amines to a sulfite-containing aqueous medium for reducing the oxidation of sulfite to sulfate therein. The sulfite-containing medium with the polyethyleneamine additive is thus useful in wet scrubber systems for sulfur dioxide absorption from a gas containing the same.
It is also known from U.S. Pat. No. 4,342,733 to use a topping agent selected from the group consisting of polyphosphate compounds and organophosphonic acid compounds in a scrubbing liquor to supplement and enhance the antioxidant activity of sulfite antioxidant agents such as the linear polyethyleneamines and substituted secondary and tertiary aromatic amines.
One problem with the polyethyleneamine sulfite antioxidants employed in the prior art is that the polyethyleneamines are generally volatile to some extent, particularly the lower molecular weight polyethyleneamines such as triethylenetetramine and tetraethylenepentamine. This results in process losses from the sulfur dioxide scrubbing system and can also pose an odor problem. In addition, such amines can be difficult for waste water treatment systems to tolerate, and therefore, disposal of spent scrubbing solution from systems employing the polyethyleneamines is complicated. For example, the lower molecular weight polyethyleneamines are not retained on ultrafiltration membranes.
Another problem with the polyethyleneamines as additives for sulfite oxidation inhibition is that they readily complex with metals, and it is necessary to add additional quantities of the polyethyleneamines to the scrubbing liquor when metals and other cations are present in the scrubbing liquor. Since the oxidation of sulfite to sulfate is trace-metal catalyzed, and suppressed by metal complexing agents as described in Huss, Jr., et al., J. Amer Chem. Soc., v. 100, p. 6252 (1978), an explanation for the anti-oxidant properties of such polyethyleneamines is that they complex with any metal ions which may be present in the scrubbing liquor to inhibit such catalysis, and do not function as true antioxidants.
It is known from U.S. Pat. No. 4,530,704 to use a process for selectively removing and recovering sulfur dioxide for a gas stream containing the same by contacting the gas with absorbent (aqueous piperazine, piperazinone or a morpholinone) and thermally regenerating the absorbent (releasing the sulfur dioxide) for reuse in the contacting step.
It is also known from U.S. Pat. No. 4,783,327 to use a method of removing sulfur dioxide from a gas stream containing the same by absorbing the sulfur dioxide in an aqueous solution containing a 4-(2-hydroxyalkyl)-2-piperazinone compound or alkyl or aryl substituted derivative thereof. These compounds provide an absorbent solution which is less subject to loss during the regeneration step and yet effectively removes the sulfur dioxide from the gas stream without interference from other associated gases.
In commonly assigned application Ser. No. 569,117, filed Aug. 16, 1990, entitled "Process for Absorption of Sulfur Compounds from Fluids," (applicants Dane Chang and Steven H. Christiansen), there is disclosed a process wherein sulfur dioxide is removed from a fluid containing SO.sub.2 by employing as an absorbent for the SO.sub.2 an aqueous solution of a compound represented by the formula: ##STR1## wherein each Y is independently --(CR.sup.2.sub.2)--, --(CR.sup.2).dbd. or --(C=O)-- and each R.sup.1 and R.sup.2 is independently hydrogen; an alkyl group; a hydroxyalkyl group; an aldehyde group; a carboxylic acid group or salt thereof; or an alkyl group containing at least one carboxylic ester, a carboxylic acid or salt thereof, ether, aldehyde, ketone, or sulfoxide group; wherein the compound has at least one carbonyl group. Representative of such absorbents are 2-piperidone and ethyl piperidone 2-carboxylate.
In commonly assigned application Ser. No. 569,120, filed Aug. 16, 1990, entitled "Process for Absorption of Sulfur Compounds from Fluids" (applicants Steven H. Christiansen, Dane Chang and Druce K. Crump), there is described a process wherein sulfur dioxide is removed from a fluid containing SO.sub.2 by employing as an absorbent therefore an aqueous solution of a compound represented by the formulae: ##STR2## wherein each R.sup.1 and R.sup.2 is independently hydrogen; an alkyl group; a hydroxyalkyl group; an aldehyde group; a carboxylic acid or salt group; or an alkyl group containing at least one carboxylic ester, carboxylic acid or salt, ether, aldehyde, ketone or sulfoxide; and wherein at least R.sup.1 or R.sup.2 is carbonyl-containing group, such as an aldehyde group, a carboxylic acid containing group, a carboxyl ester group, or a ketone-containing group; or ##STR3## wherein each R.sup.3 is independently hydrogen; an alkyl group; a hydroxyalkyl group; an aldehyde group; or a carboxylic ester, a carboxylic acid or salt, ether, aldehyde, ketone or sulfoxide group. Representative of such absorbents are ethyl-1-piperazine carboxylate, 1,4-diformyl piperazine, 1-succinyl piperazine, glycine anhydride, and 1,4-dimethyl-2,5-piperazinedione.
In commonly assigned application Ser. No. 569,091, filed Aug. 16, 1990, entitled "Process for Absorption of Sulfur Compounds from Fluids" (applicants Steven H. Christiansen, Dane Chang and David A. Wilson), there is described a process wherein sulfur dioxide is removed from a fluid containing SO.sub.2 by employing as an absorbent therefore an aqueous solution of a compound represented by the formula: ##STR4## wherein X is --O--, --NR.sup.1 --, or --N.dbd.; each Y is independently --(CR.sup.2.sub.2)--, --(C.dbd.O)--, --O--, NR.sup.1 --, --N.dbd., or --C(R.sup.2).dbd.; each R.sup.1 and R.sup.2 is independently hydrogen; an alkyl group; a hydroxyalkyl group; an aldehyde group; a carboxylic acid or salt group; or an alkyl group containing an aldehyde group, a carboxylic acid or salt group, ketone, carboxylic ester, ether, or sulfoxide group; and m is an integer, preferably of from 2 to about 4. Representative of such absorbents are hydantoin, N.sup.2,N.sup.3 -dimethylpropyleneurea, trialkyl-1,3,5-triazine-2,4,6(1H,3H,5H)trione, and 2-oxazolidone
In commonly assigned application Ser. No. 569,118, filed Aug. 16, 1990, entitled "Process for Absorption of Sulfur Compounds from Fluids" (applicants Dane Chang, Steven H. Christiansen and David A. Wilson), there is described a process for removing SO.sub.2 from a fluid containing SO.sub.2 by employing as an absorbent for the SO.sub.2 an admixture of water and a compound represented by the formula: ##STR5## wherein each R.sup.1, R.sup.2 or R.sup.3 is independently hydrogen; an alkyl group; a carboxylic acid group; a hydroxyalkyl group; an aldehyde group; or an alkyl group containing a carboxylic ester, a carboxylic acid or salt, ether, aldehyde, ketone or sulfoxide group; wherein at least one of R.sup.1 and R.sup.3 is a carboxymethyl group and at least one of R.sup.1 and R.sup.3 is hydrogen, preferably at least one R.sup.1 is carboxymethyl and at least one R.sup.3 is hydrogen. Representative of such absorbents is symmetrical ethylenediaminediacetic acid.
It is known from U.S. Pat. No. 4,324,775 to use a water-immiscible organic solution of a hydrophobic primary, secondary, tertiary or quaternary amine salt as a sulfite transfer agent for contacting an SO.sub.2 -pregnant aqueous alkali SO.sub.2 scrubbing solution to enhance SO.sub.2 scrubbing. The organic solution is subsequently heated to release SO.sub.2 in a stripping step, and then recontacted with the aqueous alkali scrubbing solution to regenerate the aqueous solution for recycle to the scrubbing step wherein gaseous SO.sub.2 is contacted with the regenerated aqueous alkali SO.sub.2 scrubbing solution.
Other sulfur dioxide absorption solvents, buffers and methods are described in various references, such as, for example, U.S. Pat. Nos. 4,387,037; 4,363,791; and 3,873,673.